What Could Cause Rectal Grumble?

Hello I am 16 years old recently I have experienced a loud rumbling noise coming from my back passage. It feels like it is inside my rectum. It started when I had diarrhea once, I passed mucus and my stools were black and oily. After that the rectal grumbles started, I am not constipated. Then I began to get thin stools and aches inside my anus, the doctor said I had hemorrhoids I used rectal ointment for that and it stopped. Then one night I couldn't sleep because my bladder felt very full even though there was no urine in it, the doctor then checked if I had hemorrhoids by inserting a lubricated glove in my anus, she said she felt nothing. After I began to have spasms between my anus and vagina I think it is called perineum. I also felt a crawling sensation there aswell my mother gave me antibiotics which I took for four days I'm not sure whether that helped it or it was a nerve problem that subsided itself. Well after all that I forgot about the rectal noises because it stopped, well it has returned,the noise, and I want to know what may be the cause of the loud rectal rumbles, do you know what may be the cause of it? Please help me because it is very embaressing